1. Field of the Invention
The present invention relates generally to improvements in a device for handling stacked sheets of thin materials, such as sheets of paper. More particularly, the present invention relates to a high-speed mechanism for removing single sheets of paper from the top of a stack of sheets, where such sheets are to be transported for individual processing, such as by optical scanning, after being removed from the stack.
2. Description of the Prior Art
The use of rotating friction rollers or belts to "pick", that is to engage and remove laterally, the top sheet in a stack of sheets is known. A common problem with such mechanisms is that they do not always successfully pick a single sheet from the top of the stack, because the sheet below the top sheet tends to adhere to the lower surface of the top sheet and to follow the top sheet as it moves. In some circumstances, more than one sheet will follow the top sheet. If more than one sheet is removed from the stack, this can cause severe problems, particularly in machines that scan information contained on both sides of a sheet, e.g., a two-sided, optically scanned answer form. In higher speed machines that handle hundreds or thousands of documents in sheet form per hour, even occasional malfunctions of the sheet picking mechanism can lead to numerous errors or cause significant losses in throughput. Ordinarily, to avoid errors, immediate multiple-sheet detection must occur and operator intervention will be needed to remove multiple-picked documents and restore them to the document stack. If multiple-picked documents are not recognized, jams and/or misreading of documents can occur. The greater the picking and processing speed of the equipment, the greater the throughput loss when an operator must intervene.